Tag Archives: ecology

How big do prairies need to be?

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There is an awful lot we still don’t understand about prairies (and the rest of the natural world, for that matter).  First and foremost, we haven’t even come close to discovering all the species that live in prairies.  We have probably identified all of the birds, and most of the other vertebrates, but there are still many prairie invertebrates no one has yet described.  The world of microorganisms is beginning to open up to us, but that is still, by far, the biggest pool of unknown species.  How can we manage a natural system when we don’t even know what’s there – especially when those inhabitants have a tremendous impact on ecosystem function?

It's still possible that we'll find more snake species in North American prairies, but we've surely discovered nearly all of them. This one is a juvenile eastern racer (Coluber constrictor) in TNC's Platte River Prairies, Nebraska.

It’s possible that we’ll find more snake species in North American prairies, but we’ve surely discovered nearly all of them. This one is a juvenile eastern racer (Coluber constrictor) in TNC’s Platte River Prairies, Nebraska.

We need to discover more species and understand the basics of their life histories, but there are some other really big prairie questions out there that need attention as well.  I thought I’d share a few of the ones I think are most important.  I’m hoping you’ll find them thought-provoking and join me in trying to chip away at them.  We’re not going to answer any of them in the near future, but more people thinking about them and making careful observations will speed us more quickly along the path.  Because each question takes some explaining, I’ll just deal with one here and cover the others in future posts.

Big Question #1:  How big and connected does a prairie landscape need to be to support the majority of prairie species and essential natural processes?

This one has bothered me for a long time because not knowing the answer prevents us from setting reasonable goals for landscape-scale conservation efforts.  As prairie landscapes get carved up by rowcrop agriculture (e.g., the Dakotas), how do we know how much fragmentation will be catastrophic to the ecosystem?  On the flip side, in landscapes that were carved up long ago, what size prairie restoration projects should we aim for to truly restore sustainable prairie ecosystems?

We know that some prairie species require large patches of habitat.  Based on quite a bit of research on birds, we can make reasonable guesses about the size of prairie landscape needed to maintain populations of most bird species.  I’m not completely up to date on this research topic, but I think it’s fair to say that if you had a couple thousand acres of prairie and managed it for a diversity of habitat structure, you’d see most of the grassland bird species in your region show up to nest.  To ensure that those populations were large enough to survive tough years, it’d be nice to have more like 5,000 or 10,000 acres.  Depending upon where you live, that might sound like an impossibly big number or a very manageable one (Illinois doesn’t even have 10,000 acres of remnant prairie in the state, while 10,000 acres is pretty small for a ranch in the 12 million acre Nebraska Sandhills).

Uplan

Upland sandpipers are found most often in larger prairies, especially those with relatively short vegetation.

Assuming that 10,000 acres is a comfortably large prairie for grassland birds, you might think we could just use that as a benchmark for other species as well.  Unfortunately, there are a number of problems with that assumption, many of which I laid out in an earlier post.  One big problem is that bird habitat (quantified largely by factors like vegetation structure and insect abundance) is not necessarily quality habitat for pollinators, ants, or many other species that rely on high plant diversity.  Each of those other species has particular needs, both for habitat size and habitat quality.

A few species (bison? prairie dogs? others?) might need considerably more than 10,000 acres to support a viable population.  However, many other species probably need considerably fewer.   In fact, 10,000 acres might seem like an entire universe to many invertebrate species – although the more we learn about insect migrations, the more complicated that picture becomes.  Is 10,000 acres enough to provide for the vast majority of prairie species?  Maybe.  We really don’t know.

Green darners, and many other dragonfly species, migrate long distances. So do a number of moths and butterflies. Other invertebrates can also travel long distances. Does that make them more or less reliant on large prairie blocks?

Green darners, and many other dragonfly species, migrate long distances. So do a number of moths and butterflies. Other invertebrates can also travel long distances. Does that make them more or less reliant on large prairie blocks?

Regardless of whether or not it’s big enough to sustain populations, we know that restoring and/or preserving a single 10,000 acre block of prairie somewhere in the central United States would not be sufficient to conserve all prairie species.  In order to preserve genetic health and allow populations to recover from catastrophic events, species need multiple habitats in multiple locations.  They also need connectivity between those habitats so that individuals can move between populations.  So, we will need multiple examples of large prairie blocks in every region of the country, with smaller prairies around and between them.  (Questions about what constitutes connectivity and how much connectivity each species needs are also big important questions, but before we address those, we first need to know how large individual habitat blocks need to be.)

Why is this so important?  I’ll give you two real world examples.  First, think about a prairie landscape that has been relatively intact for thousands of years, but is now becoming fragmented by a rapid increase in new rowcrop agriculture.  This is a situation all too familiar to conservationists in the Dakotas, where millions of acres of prairie have been converted to rowcrops over the last couple of decades.  As those conservationists struggle to protect remaining prairie through conservation easements and other strategies, they are doing so with limited time and money.  Knowing what size a prairie block needs to be to sustain species and ecosystem processes would be tremendously helpful.

Let’s say an organization obtains a conservation easement that prevents 5,000 acres from being farmed.  Should they prioritize obtaining an additional easement next to it so that if everything else in the county gets farmed up, there will still be a 10,000 acre block of prairie remaining?  What if they have to pay double the price to obtain that second easement?  Is it worthwhile?  Or should they spend the same amount of money on two more 5,000 acre easements in other locations?  Not knowing the answer to what seems a pretty basic question makes it really difficult to know how to proceed.

My second example is at the other end of the spectrum.  There are a number of large scale prairie restoration efforts going on around North America, where thousands of acres of cropland are being restored to high-diversity prairie communities.  The best of those start with a number of unplowed prairie fragments and enlarge and reconnect those through restoration. The complexes of interconnected remnant and restored grassland they build are many thousands of acres in size.  The Nature Conservancy’s Glacial Ridge project in Minnesota, Nachusa Grasslands in Illinois, and Kankakee Sands project in Indiana are all great examples of this, as is the US Forest Service’s Midewin Tallgrass Prairie in Illinois.

We have proven that we can rebuild prairie landscapes of 10,000 acres and larger.  The sites look good, with beautiful plant communities and abundant wildlife, but are they big enough to sustain that biological diversity?  Should those sites be spending $15,000 per acre to buy high-priced cropland around their borders and increase the size of their restoration projects? Or should they invest those funds in invasive species control and other management needs to protect the investment they’ve already made?

Unfortunately, the answers to these fairly simple questions are not going to be simple to obtain.  We and others have taken a few baby steps by comparing the diversity and abundance of invertebrate species among prairie fragments of varying sizes and degrees of isolation, but we’re just getting started.  I think a better approach would be a large collaborative project that focuses on some of our largest, most intact prairie landscapes such as the Sandhills of Nebraska and the Flint Hills of Kansas and Oklahoma.  Studying how populations and ecosystem processes differ between core areas of those landscapes and the fragmented edges would be an excellent start.  We could learn which species might be most vulnerable to the negative impacts of fragmentation, and then focus on those species through additional research looking at how they are doing in prairies of varying sizes across their ranges.

We can learn a lot by studying how species do in the core versus the ragged edges of huge intact prairie landscapes like the Nebraska Sandhills.

We can learn a lot by studying how species do in the core versus the ragged edges of huge intact prairie landscapes like the Nebraska Sandhills.

I’ve planted this idea with quite a few people, but nothing has really taken off yet.  I’m not giving up.  This is too important.  Does anyone have a couple million dollars to spend answering one of the most pressing conservation questions of our time?

…

Here are a couple other examples of big research questions I think about.  I’ll address them in more detail in future posts.

1. How effective is prairie restoration (converting cropfield to high-diversity prairie plant communities) at defragmenting prairie landscapes?  Do populations of plants, insects, and wildlife in small prairie fragments grow larger and more interconnected when surrounding cropland is converted to prairie?  What are the key ecosystem components that need to be restored in order for that to happen?

2. How do prairie species respond to fire and grazing management patches, and how should that affect the scale and frequency of those management treatments?  What happens to a vole or other creature living in the unburned patch of a prairie when that patch burns?  Can it travel to other suitable habitat?  How does it know where to go?  What kinds of habitat can it cross and how far can it travel?

3. How does plant diversity influence the productivity and sustainability of grasslands, especially in ways that directly influence agricultural production?  Why should a rancher care about the plant diversity of his/her pasture?  Are there demonstrable increases in soil health, pollination services, forage productivity, forage selection, etc., and are those strong enough that a rancher would trade slightly lower annual income for them?

 

Ruminations on Tree Planting and Prairie Conservation

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Trees are great, but trees in and around prairies can negatively impact habitat quality for many grassland plant and animal species and provide points of introduction for invasive species.  Encroachment by trees has become a major threat to prairie conservation in many landscapes.  

A few months ago, I cut across the courthouse lawn on my way home from the office (I was walking – it’s a small town).  On the west side of the courthouse, there are a number of statues and other monuments memorializing veterans of various wars.  In the midst of those, however, is a very different kind of memorial (pictured below).  This plaque-on-concrete memorial got me thinking – yet again – about our relationships with trees, our desire to plant and care for them, and how that affects our former, current, and future relationship with prairie.

We love trees so much, we use them to memorialize important events and people in our lives. Sometimes, we then create memorials to honor people who plant trees!

We love trees so much, we use them to memorialize important events and people in our lives. Sometimes, we even create memorials to honor the trees and the people who planted them!

I live in Nebraska, home of Arbor Day.  Early European settlers of Nebraska were enthusiastic tree planters for both practical and aesthetic reasons; our legislature even designated us as “The Tree Planters State” back in 1895.  There were good reason for all that tree planting.  It’s certainly nice to have shade around one’s house and yard, and a grove of trees provides a valuable shield from strong winter winds for both homes and livestock.  In addition, early settlers found the open prairie lacked adequate wood for fuel and building materials.  However, despite the numerous practical uses for trees, I think most tree planting was and is done primarily as a way to make the landscape more visually appealing.  People just like trees.

This brings me to my contemplation of tree planting and prairie conservation.  Research has shown that when given a choice, people seem most attracted to the aesthetics of a savanna-like landscape – one with scattered trees and short grass.  That mindset is evident in the way we design our yards and parks.  Not only do we enjoy having trees, we really like to plant them ourselves.  We gain immense satisfaction from the simple act of digging a hole and plopping a seed or small seedling in the ground, knowing that we and future generations will be able to watch that tree grow skyward.  The trees we plant often become almost family members in the way we celebrate their growth and mark time by how big the trees were when such and such happened.

The landscaping around the Hamilton County, Nebraska courthouse (where the above plaque is located) is a great example of the kind of scattered trees/short vegetation landscape humans find aesthetically appealing.

The landscaping around the Hamilton County, Nebraska courthouse (where the above plaque is located) is a great example of the kind of scattered trees/short vegetation landscape humans find aesthetically appealing.

This brings up two issues for those of us working to conserve prairies.  First, we’re starting from a handicapped position when we advocate for prairie conservation because prairies are not what most people visualize when they think of natural beauty.  Given the choice between a treeless grassland and a park-like landscape dotted with trees, most people would choose the wooded park as a site to photograph, hike or picnic, or build a house.  In fact, there are countless examples in which people buy a small patch of prairie for a recreational property and immediately plant numerous trees to make it “look nicer.”  We really haven’t changed much from our European settler predecessors in that regard.

Second, we haven’t yet found a prairie-related analog to tree planting; a simple activity that creates something people can take ownership of, love and nurture.  Planting trees is so easy a child can do it, and with very little investment of time or money, someone can establish a couple trees that become treasured landmarks or memorials – – which further reinforces people’s love of trees and wooded areas.  In contrast, planting prairies is fairly complicated and requires more space.  It also takes a few years for a planting to grow out of its weedy phase and start to look like a prairie.  Prairie planting can certainly be rewarding, but it’s not nearly as simple, accessible, and instantly gratifying as tree planting.

Many people find wide expanses of open prairie impressive, but not alluring. How do we get people to care about and nurture landscapes and ecosystems they have to work to appreciate?

Many people find wide expanses of open prairie impressive but not alluring. How do we get people to care about and nurture landscapes and ecosystems they have to work to appreciate?

So how can we help people connect with prairies in the same way they connect with trees and wooded landscapes?  I don’t have all the answers, but here are a few ideas.

1) We need to encourage more people to spend time in prairies and make sure they enjoy themselves when they go. It can be a definite challenge to convince someone to take a walk in a prairie.  Even worse, when people do step foot in a prairie, many are unimpressed because they don’t really know what to look for or how to appreciate what they’re seeing.  As a result, they often walk away with an even less favorable opinion than before they came.  “It was just a lot of grass!  And I was pulling ticks off myself all night!”

A good naturalist and interpreter can lead someone on their first prairie excursion and make it a positive and thought-provoking experience.  There is no substitute for the expertise and enthusiasm of a good leader, but there aren’t enough of those people to go around.  Several Nebraska Master Naturalists approached me last year with an idea to create a “Prairie Exploration Guide” – a pamphlet/booklet designed to help newcomers to prairie see the beauty and complexity they might otherwise miss.  The guide is still in the development stage, but I have high hopes that it will be a useful tool when it’s done.

2) Using native prairie plants in landscaping is becoming increasingly popular. The public’s concern over population declines of bees and monarch butterflies is helping to spur the movement, as are issues such as water conservation.  There is no question that getting the public to buy, plant, and appreciate native prairie plants in their backyards is a major step toward building a prairie conservation constituency – and backyard prairie gardens also make real conservation contributions on their own.  Significant obstacles still hinder the movement, especially our cultural norms about what yards and gardens are “supposed” to look like, but I am optimistic about the future.

3) One successful method for engaging people in prairie conservation at our Platte River Prairies has been through seed harvesting. People identify with both the value of seeds and the idea of restoring lost habitats.  Harvesting seed is a tangible way people can contribute toward something important; they can measure that contribution by the amount of seed piling up in their buckets.  Ideally, harvesters come back and help plant the seed they picked, and then visit regularly to watch the prairie planting develop over time.

I hope that helping me harvest and plant seeds at our family prairie will help my kids develop a love for grasslands.

I hope that helping to harvest and plant seeds at our family prairie will help my kids develop a love for grasslands.

Along those lines, one of the most inspired strategies I’ve seen to engage people in prairie restoration was being done by Wayne Pauly in Dane County, Wisconsin.  I went on a tour of some of his prairie restorations back in 2004 and was very impressed with both his plantings and his involvement of volunteers. Most particularly I liked Wayne’s strategy of having volunteers “paint the prairie” with seeds during prairie plantings.  He’d give each volunteer a bucket of seeds of one prairie wildflower species and let them decide how and where to plant those seeds – allowing them to create a pattern or design of their choice (thus the idea of “painting”).  That is a brilliant idea, and one that should not only be fun on planting day, but should also draw those volunteers back in subsequent years to view the results of their work.

Humans have a long and strong relationship with trees, one that is likely embedded within our DNA.  Tree planting is an easy, accessible, and tangible way to contribute something to the natural world.  Unfortunately, tree planting doesn’t do anything to help prairies, and can sometimes be counterproductive if trees are planted in or near open grassland.  If prairie conservation is to succeed, we need to get the public excited about grasslands and combat the perception that prairies would look a lot prettier if they just had some trees growing in them.  More importantly, we need more strategies that actively connect people with prairies and give them the same sense of fulfilment they get from planting trees.  I think we’re getting better, but we have a long way to go.